1. Field of the Invention
The present invention relates to radio frequency communications systems, and more particularly to a method for routing frequency hopping signals to antennas in a multiple carrier communications system.
2. Description of the Prior Art
Communication systems must be able to simultaneously broadcast and receive multiple radio frequency (RF) signals that share the same frequency spectrum while being susceptible to very little system degradation. This entails isolating the transmit and receive functions of the communication system, as well as, in the case of multiple transmit antennas, isolating each transmit antenna from the other transmit antennas when more than two channels are simultaneously transmitting. Isolation may be accomplished through techniques such as phase cancellation, frequency separation, and spatial separation. Spatial separation mandates that not only the transmit and the receive antennas be separated, but also that the multiple transmit antennas be separated from each other.
Achieving isolation between the antennas in a communication system is extremely difficult since there always is a signal path between the antennas, commonly referred to as a xe2x80x9cback door pathxe2x80x9d. The existence of this path makes the communication system susceptible to the deleterious effects caused by intermodulation products that may be within the transmit filter bandwidth. Intermodulation products are radiated frequencies produced by coupling of two or more carriers between the multiple transmitter amplifier outputs and also by two different frequencies combining at proximate non-linear junctions. To improve system performance these intermodulation products must be reduced, in essence by reducing the frequency mixing products that fall within adjacent receiving or transmitting channels of the system. This enables the receiving antenna to receive the relevant transmitted signals and also enables each separate transmitting coupler and antenna combination to radiate relatively clean frequencies.
What is needed, therefore, is a method of routing frequency hopping signals to one of two transmitting antennas in a multiple carrier communication system so as to minimize the production of intermodulation products and to improve system performance.
The preceding and other shortcomings are addressed and overcome by the present invention which provides generally, a method of routing a frequency hopping signal to one of two transmitting antennas in a multiple carrier communication system. Briefly, the method comprises storing known a-priori information regarding frequency hopping signal assignments, scanning a transmitter frequency and antenna path assignment table to determine the closest existing transmitting frequency and its antenna to the frequency hopping signal to be assigned, assigning the frequency hopping signal to an available path on the other antenna, and updating the transmitter frequency and antenna path assignment table. In addition the method includes determining whether the assigned path on the other antenna conflicts with existing frequency assignments, and preempting the antenna assignment when a conflict exists.